The bombesin-like peptides are a large family of peptides originally characterized in frog skin, but later found to have wide distribution and potent physiologic effects in mammals. One mammalian homolog of bombesin is gastrin-releasing peptide (GRP). GRP is widely distributed in the GI tract and CNS; but of greatest clinical importance, high levels of GRP are expressed in fetal lung and by most small cell lung carcinomas (SCLC). While the expression of GRP in human fetal lung is well documented, and the ability of GRP to stimulate cellular proliferation and air way development in vitro has been demonstrated, the role of GRP in lung development is not yet clearly understood. More importantly, critical in vivo experiments to explore the therapeutic potential of GRP to stimulate lung development have not been performed. This stems from the fact that rodents do not show the same pattern of GRP expression in developing lung that humans do. Our laboratory recently demonstrated that rhesus monkeys express GRP in developing lung in a similar pattern as humans and additionally, that in organ culture of fetal rhesus monkey lung, GRP markedly stimulates airway growth (1). In organ culture, treatment of 60 days gestation fetal monkey lung with 10 nM bombesin causes an increase in airway size and number to that seen in 80 day gestation lung. This striking effect on airway development suggests that GRP has potential therapeutic roles in very early premature deliveries. Because the pattern of GRP expression in developing lung appears highly primate specific, this phenomenon can only be studied in primates. While the in vitro data from our laboratory points to significant effects, before funding for a full scale study in vivo can be requested, further data demonstrating feasibility and efficacy of administering GRP and GRP antagonists to monkeys in utero must be demonstrated. Thus it is the purpose of this application to perform experiments to optimize in utero administration of peptides and antagonists and generate preliminary data of their effects on lung development. It is also the purpose of this application to further develop organotypic culture of fetal monkey lung to allow characterization of the regulation and action of GRP and GRP receptor expression in fetal lung. This study will be performed in two phases. The first phase will determine optimum dose and route of administration of GRP or stable agonists and antagonists. Levels of peptides present in amniotic fluid will be determined to aid in estimating dosage. Next peptides will be administered to the fetus either ip or into the amniotic fluid, and the fetus analyzed to determine peptide distribution and stability. Based on these preliminary experiments, an appropriate route of administration will be determined and the effects of 5 day infusions of peptide add antagonist on lung development determined. Both acute and chronic effects will be studied by morphologic, immunochemical and molecular techniques. Next, the role of endogenous bombesin-like peptides on airway development will be determined by administering specific bombesin antagonists. The effects observed in vivo will be correlated with in vitro studies to precisely localize the cells which respond to GRP. In vitro studies will be aimed at developing methods to characterize GRP induced signalling events and to characterize hormonal regulators of GRP synthesis and secretion. These studies will provide the first data on the ability of bombesin to regulate airway development in primates and provide sufficient data to form the basis of an NIH RO1 application. These studies will be made practical by the expertise of the ORPRC in fetal-maternal studies and the results will likely have important implications for the treatment of highly premature infants.